Countries keep stealing blueprints and do other actions towards me (Soviet Union, 1939) and my intelligence level has not been changed since I started '33 (it's on 10) what the hell am I supposed to do? Raise the intel level?
Yeah, the SU is targetted by numerous countries, so you have to deal with it. Raise you intel level if you wish; but I don't see the harm in stealing a blueprint or two here and there. (Besides, I find they just end up wasting money anyway with the success rates.)
Once you get your intel to level 10 your internal defenses are as good as they are going to be. Anything above 10 increases your chances of success in foreign intel.
Are you sure about this? I definitely recall seeing my own defense efficiency go up as I raised my intel above 10. You shouldn't have bad spy events happening all that often at all, really, I never do, but I also max my intel every chance I get.
Yep, playing as the German Republic in AAR (tonight) I raised my intel above level 10 but it never raised my domestic intel above ~81.67%. Moving towards a closed society should also increase that percentage some.